An image sensor is a semiconductor device that converts images into electric signals. An image sensor may be classified a charge coupled device (CCD) image sensor and a complimentary metal oxide semiconductor (CMOS) image sensor.
The CCD image sensor may include a plurality of metal oxide semiconductor (MOS) capacitors, and the MOS capacitor operates by transferring carriers generated by light. Meanwhile, the CMOS image sensor may include a plurality of unit pixels and a CMOS logic circuit controlling output signals of each unit pixel.
An image sensor may include a substrate, a red photodiode, a green photodiode, a blue photodiode, a plurality of plugs for transferring signals generated from each photodiode to a surface of the semiconductor substrate and a transistor for transferring signals.
In the image sensor having the above structure, isolation between the photodiodes may become an important factor as the size of pixels is reduced. Thus, an isolation region may be formed by doping impurities for facilitating electrical isolation between the photodiodes, and a thermal process may then be performed for stabilizing the doped impurities. In this case, a lateral diffusion of the doped impurities may occur. However, in order to form the isolation region by the doped impurities, an additional mask must be fabricated. In addition, the lateral diffusion of the impurity ions occurs during the subsequent heat process, so the doping profile is changed. Accordingly, the isolation region may not sufficiently perform its function, exerting a bad influence on the image quality.